P2419HC, multiple questions/issues

Auto Select for USB Type-C doesn't work with MST enabled
Input source -> Auto Select disabled if MST active. Why and how to fix?
* Working as designed. The act of enabling MST removes the Auto Select
for USB-C

DisplayPort Alternate Mode (Alt Mode) for USB Type-C
How to use DisplayPort Alternate Mode instead HDMI for USB Type-C connections to have MST? By default HDMI used now (if supported).
* You lost me on that question. HDMI and MST daisy chain cannot be used. MST daisy chain can only be used with USB Type-C and DP.

* Laptop has its AC power cable connected
* Laptop lid is closed
* Laptop TB3/USB Type-C --> P2419HC USB Type-C to C cable --> P2419HC USB Type-C in port (Menu- Display- MST On)
* P2419HC DP out port --> P2419HC DP to DP cable --> second monitor DP in port

* PC DP out port --> P2419HC DP to DP cable --> P2419HC DP in port (Menu- Display- MST On)
* P2419HC DP out port --> P2419HC DP to DP cable --> second monitor DP in port (Menu- Display- MST Off)

How to switch off blue, green, red, white flashing if no signal? How to switch off Debug Window which displayed on click Button1?
* That sounds like you somehow went into the Dell internal only FSM (Factory Service Menu) and turned Burn-in on? Were you in the Dell internal only FSM?

How to disable self-test options and take firmware back? How to upload newer firmware because I downgraded it by mistake in process of solving my issues? Now I have M3B106 instead of M3B109.
* You cannot. Dell never posted M3B109. I cannot think of any way that we could have made it clearer that it was 106?

>> DisplayPort Alternate Mode (Alt Mode) for USB Type-C
How to use DisplayPort Alternate Mode instead HDMI for USB Type-C connections to have MST? By default HDMI used now (if supported).

> * You lost me on that question. HDMI and MST daisy chain cannot be used. MST daisy chain can only be used with USB Type-C and DP.

Yes I know that HDMI can't use MST. I want use it with USB Type-C. But Type-C is just a port and it have both HDMI and DisplayPort implementations. My host device support both and I have full-featured cable. I don't know why but HDMI mode selected by default.

> Laptop TB3/USB Type-C --> P2419HC USB Type-C to C cable --> P2419HC USB Type-C in port (Menu- Display- MST On)
> P2419HC DP out port --> P2419HC DP to DP cable --> second monitor DP in port

Yes, but I use Samsung Note10+ instead laptop.

> How to switch off blue, green, red, white flashing if no signal? How to switch off Debug Window which displayed on click Button1?
>> That sounds like you somehow went into the Dell internal only FSM (Factory Service Menu) and turned Burn-in on? Were you in the Dell internal only FSM?

This mode was turned on after firmware upload. I didn't any additional for that.

> Dell never posted M3B109. I cannot think of any way that we could have made it clearer that it was 106

Versions changing history same as there https://www.dell.com/community/Monitors/P2419HC-downgraded-firmware-from-M3B109-to-M3B106/m-p/7506598

Sorry but screenshot of FW progress in Russian. But you can see versions

FW progress

Debugger window which I don't want to see.

UPD. This part solved. Just "BURNIN" switched to off and display restarted. Thanks